Evaluation of a Real-time PCR-based Assay Using the Lightcycler System for Detection of Toxoplasma Gondii Bradyzoite Genes in Blood Specimens From Patients With Toxoplasmic Retinochoroiditis

Int J Parasitol. 2005 Mar;35(3):275-83. doi: 10.1016/j.ijpara.2004.11.016. Epub 2005 Jan 18.


PCR based methods have advantages over traditional methods for the diagnosis of toxoplasmosis, especially when serology fails and clinical symptoms are not evident. However, current PCR-based assays are often labour-intensive and not readily quantifiable and have the potential for contamination due to a requirement for postamplification sample handling. Real-time PCR can address these limitations. We have developed and evaluated a highly sensitive Real-time PCR (Light-cycler, LC-PCR) to detect and quantify Toxoplasma gondii B1 and bradyzoite specific genes (SAG-4, MAG-1) in serum and peripheral blood mononuclear cells (PBMC) specimens, from five immunocompetent subjects with clinically suspected toxoplasmic retinochoroiditis (TRC) or without a suspected T. gondii infection. A standard curve for quantitation of parasitic load was generated using SYBR Green I fluorescent detection. The results were compared with those obtained with a nested PCR (n-PCR). In TRC patients, both PCR methods confirmed ophtalmoscopy and fluorangiographic findings. Among the TRC patients, the use of LC-PCR was more sensitive than n-PCR for detection and quantification of either B1 gene (P<0.001) or SAG-4/MAG-1 gene (P<0.05). LC-PCR has been shown particularly useful to accurately determine the parasite DNA load in follow-up specimens in whom the performance of either B1 or SAG-4 and MAG-1 in detecting T. gondii loads, varied with respect to specific antitoxoplasmic treatment.

Publication types

  • Evaluation Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Animals
  • Chorioretinitis / diagnosis*
  • Chorioretinitis / parasitology
  • DNA, Protozoan / isolation & purification
  • Female
  • Genes, Protozoan
  • Humans
  • Male
  • Middle Aged
  • Polymerase Chain Reaction / methods
  • Sensitivity and Specificity
  • Toxoplasma / genetics*
  • Toxoplasmosis, Ocular / diagnosis*


  • DNA, Protozoan